Cisco Unified CallManager Attendant Console integrates traditional
time-division multiplexing (TDM) telephony functions with advanced IP telephony
applications and services, such as Lightweight Directory Access Protocol (LDAP)
directory. A primary benefit of Cisco Unified CallManager Attendant Console
over traditional attendant-console systems is the ability to monitor the state
of every line in the system and to efficiently dispatch calls.

The information in this document is based on these software and
hardware versions:

Cisco CallManager 4.x

Cisco Attendant Console 1.4

The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.

There are three types of communication between the AC client and
server:

AC client to Remote Method Invocation (RMI)—The
client always connects to RMI at server ports 1099 through 1129. Then, the
server tells the client to establish a second TCP session with the server on a
second TCP port. This port is randomly taken and there is no way to guarantee
that a particular TCP port is always used.

AC client to Line State Server (LSS)—In this case,
there is UDP LSS traffic that comes from the servers. This can be fixed in the
Advanced Settings dialog box (see the Solution to Receive
Line Status Across a Firewall section). The ports specified in the
Services Parameters dialog box are used by Cisco CallManager to listen to
Termination Call Detail (TCD) requests, initialize the AC clients and offer
line state information to the clients. These TCP ports must not be
changed.

A firewall is not supported because the AC uses random ports for RMI
connections. Only one available port is used to initiate the RMI connection,
which starts with 1099. After the RMI connection is established, RMI uses a
random TCP port (normally the first available port). Therefore, make sure any
one the TCP ports is open in the 1099 through 1129 range. If these random ports
are not open, the AC fails with this error message:

error communicating with the server

Refer to these documents for more information about the Cisco
CallManager TCP and UDP port usage for Attendant Console:

In a Cisco Attendant Console, the line-state and call-forwarding status
of the primary line of each user is presented with each record entry. When you
use Cisco CallManager and Attendant Console across Network Address Translation
(NAT) interfaces, or when a firewall is between them, TCP traffic works
correctly with the NAT transversal. Therefore, most of the AC functionality
works. However, the problem is for the Attendant Console line status which uses
UDP. Also, the UDP traffic from the CallManagers cannot pass through the NAT
interfaces.

Cisco Attendant Console uses UDP ports for line-state. The UDP port
that should be used can be configured in the Advanced Settings dialog box of
Cisco Attendant Console. If no port is configured, the AC uses the first
available UDP port (random).

If a free UDP port is specified, such as port 1234 (see
Figure 2), make sure this port is opened in the
firewall too.

Complete these steps in order to configure the UDP port
used:

Log in to Attendant Console.

Choose Edit > Settings.

In the pop-up window, click Advanced and change
the Local Host IP Address field to 172.16.1.1:1234 if the IP
Address of the Attendant Console PC is 172.16.1.1 and the UDP port is 1234.

Click Save.

Log out for the new settings to take effect.

Note: The AC was not designed to work with a firewall or NAT. However,
there is a feature request bug filed to lock down the port range. Refer to
Cisco bug ID
CSCee21603
(registered customers only)
for
more information.

For now, the only workaround for this issue is to either unblock
the TCP ports used or disable the firewall.